The disclosure relates generally to corrosion sensors, and more particularly, to a corrosion sensor for an internal structure of a machine such as a compressor.
Machinery and equipment operated in harsh environments are often subject to accelerated corrosion rates which, if not monitored or controlled, can result in premature aging and eventually failure of the machinery and equipment. For example, in a gas turbine, gases flow along a flow path in a compressor that compresses the gas flow. The compressor includes a number of internal structures such as blade airfoils and nozzles that may be subjects of corrosion. In particular, the constituents of air being compressed in the compressor can sometimes drive pitting creating corrosion and then initiating cracking due to the high stresses.
In some settings, corrosion sensors may be installed on metal surfaces other than the internal structure to monitor the presence and/or rate of any general corrosion. For example, a conventional corrosion sensor, which may be referred to as a ‘coupon’, may include a metal electrode similar to the metal requiring analysis or may include alternating layers of electrodes separated by dielectric material. In any event, the electrodes may have an oxidation potential comparable to that of the metal surfaces to which they are attached so that the general corrosion rate on the metal surfaces may be approximated by the general corrosion rate on the electrodes. Because conventional corrosion sensors are not stress loaded, they are not exposed to the mechanical and thermal loading, like the internal structures of concern. As a result, they are typically inaccurate to predict component failure. The only mechanism to forestall unforeseen down time in such settings is through periodic, visual inspections, which increases the down time.